Jet aircraft have become the most widely accepted form of commercial air transportation. These planes, except for the SSTs, generally fly at speeds of one-half to three-fourths the speed of sound. The gas turbine engines used to propel these planes produce large quantities of unburned hydrocarbons and suffer in performance because of their failure to utilize the energy available in this unburned fuel. This effect is due in part to the incomplete combustion of the liquid fuel, which in turn, is partly due to inadequate pre-mixing of fuel and air prior to combustion.
This problem has long been recognized, and a number of approaches and structural changes have been made to improve the premixing of fuel and air. Examples of such structures are shown in the following patents: U.S. Pat. No. 3,973,390 for a "Combustor Employing Serially Staged Pilot Combustion, Fuel Vaporization and Primary Combustion Zones"; U.S. Pat. No. 4,478,045 for a "Combustors and Gas Turbine Engines Employing Same"; U.S. Pat. No. 4,854,127 for a "Bimodal Swirler Injector for a Gas Turbine Combustor"; U.S. Pat. No. 4,938,020 for a "Low Cost Annular Combustor"; U.S. Pat. No. 5,265,425 for an "Aero-Slinger Combustor"; U.S. Pat. No. 5,277,022 for a "Air Blast Fuel Injection System"; and U.S. Pat. No. 5,341,645 for a "Fuel/Oxidizer Premixing Combustion Chamber".
A basic theoretical analysis of the small-perturbation theory is to be found in Chapter 8 of the Elements of Gasdynamics by authors H. W. Liepmann and A. Roshko, John Wiley & Sons, Inc., 1957. This theory was modified by the inventor and led to the discovery of the new phenomenon utilized in the present invention. A more complete mathematical treatment of this new phenomenon is to be found in a recent paper by the inventor. The technical literature also shows that others have studied fluid flow over a sine wave boundary (Beauchamp, Philip and Murman, Earl M., "Wavy Wall Solutions of the Euler Equations", AIAA Journal, vol. 24, no. 12 (1986), and Chang, Keun-Shik and Kwon, O. J., "Mixed Transonic Flow Over a Wavy Wall with Embedded Shock Waves", Transaction of the Japan Society for Aeronautical and Space Sciences, vol. 25, no. 70 (Feb. 1983). These studies failed to show any evidence of the phenomenon discovered by the inventor and utilized, at least partially, in the present invention.
For complete combustion, it is desirable to have the mixing of air and fuel reduced almost to the molecular level. This is difficult to attain in a jet engine because of the high velocity of the air passing through, and the very brief time available for mixing. The experimental study and invention described herein show that by utilizing this newly discovered application of a small-perturbation theory of gases, the mixing of liquid fuel and air prior to combustion may be greatly improved.